Dean Burton thought he had secured all three points for the visitors when he struck three minutes after the restart and Chairboys’ task became even more difficult 20 minutes from time when Scowen picked up two bookings in the space of four minutes and was sent off for the first time in his professional career.
However, Blues pushed forward late on and kept the ball alive in the area before Lewis’ hooked cross was met by Johnson, who emphatically headed past Sam Slocombe from six yards.
Gareth Ainsworth made four changes to his side with two those enforced as Nick Arnold came in for the suspended Marvin McCoy and Leon Johnson replaced the injured Charles Dunne with Kortney Hause switching to left-back. The other two changes saw Sam Wood and Steven Craig replacing Billy Knott and Dean Morgan.
Scunthorpe started brightly and saw plenty of the ball in the opening exchanges with Hakeeb Adelakun’s second-minute strike deflecting into the palms of Matt Ingram. Top scorer Sam Winnall was then just unable to get on the end of Deon Burton’s low cross.
Scowen had Blues’ first effort came in the ninth minute, but his strike looped harmlessly over the crossbar.
Chairboys had been slow to get into the contest, but were inches away from taking the lead in the 13th minute. Craig did brilliantly to hold off a defender and knock the ball into Matt McClure’s path, but Blues’ top scorer’s low shot from just inside the area shaved the far post.
Wood then fired at Sam Slocombe after good work from Cowan-Hall found the winger in acres of space on the left. Former Scunthorpe man Cowan-Hall had a chance of his own in the 18th minute after McClure, Wood and Craig combined to find him in the area, however, his shot was
Wanderers were enjoying their best spell of the half, but the visitors fired a warning sign in the 32nd minute and Ingram had to be at his to best to deny David Syers after the midfielder had found space inside the area.
Ainsworth was forced into his first change four minutes before the break as Craig went down holding his right leg after finding Cowan-Hall on a quick breakaway.
Deon Burton headed wide a minute later before Wood volleyed straight at Slocombe from 25 yards, and that was to be the final chance of an even first half.
Half-time: Wanderers 0-0 Scunthorpe
Scunthorpe were quick out of the traps in the second half and took the lead three minutes after the restart when Sean McAllister’s shot deflected into the path of Burton, who fired home from six yards.
Wanderers had to reshuffle on the hour when Cowan-Hall picked up an injury in crossing from the right and he was replaced by Jo Kuffour.
Wood miscued from just inside the area a minute later after Anthony Stewart had just been unable to get on the end of Arnold’s deep cross.
McClure blazed over in the 64th minute after the ball fell to him inside the area following good work from Kuffour to keep the ball in near the touchline.
The visitors came close to adding a second less than 60 seconds later when Winnall broke the offside trap and burst into the area, only for Ingram to narrow the angle and make a smart stop.
Chairboys’ task became even harder in the 70th minute when Scowen picked up his second booking in the space of four minutes for a late challenge on McAllister.
Scunthorpe were always a threat on the break and Ingram saved well from Syers’ header following Terry Hawkridge’s dangerous cross.
Blues were struggling to break down a well-organised defence with McClure and Kuffour not seeing much of the ball in dangerous area, and the visitors were making full use of their numerical advantage by retaining possession for large periods.
One such spell ended with Ingram again denying Winnall by tipping the striker’s 86th-minute effort over the bar.
Ainsworth’s final throw of the dice came a minute later with Junior Morias coming on for McClure.
Referee Fred Graham added on six minutes added time, mainly for the injury to Cowan-Hall, and Stewart headed Wood’s corner wide in the first of these.
There was to be one final chance for the Wanderers though, and they took it in the 96th minute. A period of pressure saw Blues keep the ball alive in the area and Johnson powered home a header from Lewis’ cross to salvage a point in the most dramatic of finishes.
Wanderers: Ingram, Arnold, Hause, Stewart, Johnson, Cowan-Hall (Kuffour 60), Lewis (c), Scowen, Wood, McClure (Morias 87), Craig (Morgan 41).
Subs: Horlock, Bloomfield, Knott, Kretzschmar.
Scunthorpe: Slocombe (c), Ribeiro, Nolan, Mirfin, Canavan, Hawkridge, Syers, McAllister, Adelakun (Williams 52), Burton (Spencer 88), Winnall.
Subs: Severn, Boyce, Waterfall, Esajas, Iwelumo.
Attendance: 2,882 (273 Scunthorpe)